Ligaments:Knee joint:Cruciate ligaments (anterior
Cruciate ligaments are in an extrasynovial but intracapsular location Anterior cruciate ligament * Multiple separate fascicles which spiral laterally from femur to tibia (fibers rotate externally 90°); fatty tissue is seen between fibers * Origin of ACL: Posteriorly from lateral femoral condyle at intercondylar notch * Insertion of ACL: Anteromedial tibial spine and adjacent plateau; bundles fan out at tibial attachment, forming "foot" * Function: ** Primary restraint to anterior tibial translation ** Major secondary restraint to internal rotation, minor secondary restraint to external rotation ** Minor secondary restraint to varus/valgus at full extension * Blood supply: Middle geniculate artery (pierces posterior capsule from popliteal); lesser supply from fat pad (inferior medial and lateral geniculates) * Nerve: Posterior articular (branch of posterior tibial) Posterior cruciate ligament * Appears as a single round ligament but consists of two major parts; rotates 90° from an antero-posterior alignment at femoral origin to medial-lateral insertion at posterior tibia ** Anterolateral bundle: Bulk of ligament, taut in flexion, lax in extension ** Posteromedial (oblique) bundle: Taut in extension, lax in flexion * Origin of PCL: Mid portion of medial femoral condyle at intercondylar notch * Insertion of PCL: Mid posterior tibia, 1 cm below joint line, where it blends in with posterior capsule * Function: Primary restraint against posterior translation * Meniscofemoral ligaments ** Both arise from posterior horn lateral meniscus and insert on medial femoral condyle; at least one present 70% of time ** Posterior (Wrisberg) lies posterior to PCL ** Anterior (Humphrey) lies anterior to PCL; intact ligament of Humphrey may mimic an intact PCL ** May play a role in secondary restraint to posterior instability; may stabilize lateral meniscus during flexion * Blood supply: Middle geniculate artery proximal and middle thirds; geniculate and popliteal artery base; capsular vessels through entire length. Posterior Capsule * Complex fibrous structure, augmented by extensions of adjacent tendons * Incomplete, pierced centrally by neurovascular structures * Proximal attachment: Vertical fibers attached to posterior margins of femoral condyles and intercondylar fossae * Distal attachment is to posterior margins of tibial condyles and intercondylar areas * Tendons/ligaments attach to posterior capsule to provide reinforcement ** Proximally (medially and laterally): Tendinous heads of gastrocnemius ** Posteromedial corner: Semimembranosus and posterior oblique ligament ** Posterolateral corner: Arcuate ligament and iliotibial tract ** Posterior central: Oblique popliteal ligament Spaces Within Cruciate/Posterior Capsule * Synovial membrane surrounds anterior, medial, and lateral portions of cruciates, but is reflected posteriorly from PCL to adjoining parts of joint capsule * Results in a potential space (PCL bursa or recess) ** Seen only when fluid-filled, best on coronal and sagittal planes ** Seen posterior to PCL and adjacent to lateral aspect of medial femoral condyle ** No contact between PCL recess and the proximal third of the PCL (fat is interposed) ** Communicates with medial (femorotibial) compartment of knee ** Does not communicate with lateral compartment ** If ligament of Wrisberg is present, it lies posterosuperior to PCL recess * Intercruciate recess ** Localized potential fluid collection between ACL and PCL, best seen on sagittal and axial planes ** Communicates with either lateral or medial (femorotibial) compartments